Many mining, excavation, and/or construction projects involve the removal of large amount of material beneath a ground surface, which results in underground cavities or voids. For example, an underground mining operation may remove a quantity of ore-bearing rock from an underground geological formation leaving one or more voids in the formation. These underground voids may be or become unstable and risk collapse of the ground above, causing injury to personnel and/or damage to equipment resting on the ground above the void. Further, a variety of natural phenomenon may also cause underground cavities or voids, which also can unexpectedly collapse.
In order to prevent and/or reduce the risk of collapse, known underground voids that are or are expected to be unstable may be filled with a solid material. Typically, this is accomplished by mixing a fluid or semi-fluid slurry of aggregate material and fines (e.g., cement or fly ash) and/or water together and pumping and/or gravity feeding the slurry through one or more injection points into the underground void until it is filled with the slurry. The slurry is then expected to cure and withstand loads from the ground surface above without or with a lower risk of collapsing.
However, hydraulic placement of the slurry mixture consumes large quantities of water that may be expensive and/or not be readily available at the location of the submerged void and may require a high-energy pump to maintain a sufficient flow rate to keep the slurry mixed until placed within the submerged void. Further, underground voids are often filled or semi-filled with water or other liquid. This may be due to the underground voids lying below an applicable water table for the underground void location, for example. Conventional void filling technologies are not particularly effective at displacing the water or other liquids in the void while simultaneously filling the void with the slurry mixture. For example, the slurry mixture may largely distribute within the water upon impact with the liquid surface and/or the slurry mixture may separate upon contact with the water surface (e.g., the cementious particles may largely float while the aggregate materials sink). As a result, the void may not be effectively filled with the slurry (e.g., it may have an inconsistent compressive strength due to a non-homogeneous composition of the deposited slurry mixture), thus much of the slurry mixture may be forced back up through a point of injection, and/or the slurry may not distribute horizontally within the void very effectively, thus limiting the maximum horizontal spacing of injection points.
As a result, current systems and methods for filling submerged voids or cavities are often expensive to implement and often fail to produce a desired performance in the field. This is often due to segregation of constituent materials of a filling material and resistance of the filling material to move through water-filled cavities.